1. Technical Field
The present invention relates to an improved bearing preferable for journaling the rotational portion for office automation equipments like computers and peripheral devices therefor.
2. Description of the Prior Art
The bearing apparatus is used for journaling a rotational portion such as a motor for driving the magnetic disc or discs, or a swing arm of a hard disc drive device as peripheral devices for computers. As shown in FIG. 13, the bearing apparatus includes upper and lower ball bearings 32, 33 having inner rings 32a, 33a fit and attached to a shaft 31 and outer rings 32b, 33b fit within a sleeve 34.
In FIG. 13, balls are denoted by the reference numeral 32c, 33c, ball retainers are denoted by the reference numeral 35, and a spacer is denoted by the reference numeral 36.
Upon rising the temperature of the bearing under the effect of the frictional heat generated by the rotation or operation of the bearing apparatus itself or the effect of heat energy supplied from the outside of the bearing, the components of the bearing expand into different dimensions. In the case of the ball bearings 32, 33, the order of the amount of expansion in the diametrical direction of the components is;
the outer ring greater than the inner ring greater than balls.
In other words, the spacing between the inner and outer raceways of the inner and outer rings enlarged upon rising the temperature of the bearing is larger than the amount of expansion of the balls so that the pressure applied by the inner and outer raceways of the inner and outer rings on the balls i.e. the pre-load is reduced. This causes the resonant frequency upon rotating of the bearing apparatus to vary, and in some cases the resonance with the other components of the equipment into which the bearing is incorporated is caused.
When the bearing apparatus of the prior art of the above described structure is used in the rotating portion of the motor for driving the hard disc drive device, sometimes the accuracy of writing or reading out the data is failed by the vibration of the drive device caused by the resonance with the other component such as a swing arm or a casing. There is also a possibility for generating noises caused by the vibration, and reducing the quietness of the drive device.
Provided that the difference of the amount of thermal expansion of the inner and outer rings is increased further, a clearance is defined between the balls and the raceways of the inner and outer rings, and the rotational run out of a hub of the motor and the run out of the surface of the magnetic disc or discs due to the rotational run out of the hub of the motor are generated. This will deteriorate the reliability of the hard disc drive device.
Although the balls are usually made of steel material, ceramic material may also be used for enhancing the durability thereof. In such a case, the above mentioned problem caused by the difference of the amount of thermal expansion between components will become more serious, since the amount of thermal expansion of the ceramic material is further lower than that of the steel material.
Accordingly the object of the present invention is to provide a bearing apparatus wherein an appropriate pre-load is applied constantly to the balls even if the components of the bearing apparatus expand by rising the temperature thereof. The purpose of the present invention is to provide a bearing apparatus of high rotational accuracy wherein the variation of the resonant frequency and the rotational run out caused by the variation of the temperature are reduced.
In order to achieve the purpose of the present invention, a bearing apparatus according to the first aspect of the present invention comprises
a shaft, a cylindrical outer ring member surrounding the shaft, and a plurality of balls of the first and the second rows interposed between the shaft and the outer ring member, the bearing apparatus being characterized in that:
the outer ring member includes upper and lower portions and a central portion therebetween,
two rows of outer raceways for the first and the second row of balls are formed on the inner peripheral surface of the upper and lower portions of the outer ring member,
a squeeze ring of the same material as that used in forming the outer ring member or of any other material of substantially the same factor of linear thermal expansion as that of the outer ring member is press fit around the outer periphery of the central portion of the outer ring member to elastically deform the outer ring member inwardly to form an inwardly protruding squeezed portion.
A compound bearing apparatus according to the second aspect of the present invention comprises
a shaft to which an inner ring is fit slidably, a cylindrical outer ring member surrounding the shaft, a plurality of balls of the first row interposed between the first inner raceway formed on the outer periphery of the inner ring and the first outer raceway formed on the inner periphery of the outer ring member, a plurality of balls of the second row interposed between the second inner raceway formed directly on the outer periphery of the shaft and the second outer raceway formed on the inner periphery of the outer ring member, the bearing apparatus being characterized in that:
the outer ring member includes upper and lower portions on the inner periphery of which is provided with the first and the second outer raceways respectively and a central portion therebetween,
a squeeze ring of the same material as that used in forming the outer ring member or of any other material of substantially the same factor of linear thermal expansion as that of the outer ring member is press fit around the outer periphery of the central portion of the outer ring member to elastically deform the outer ring member inwardly to form an inwardly protruding squeezed portion,
wherein the inner ring is secured to the shaft with applying an appropriate pre-load thereon.
A compound bearing apparatus according to the third aspect of the present invention including
a stepped shaft having a larger diameter shaft portion and a reduced diameter shaft portion, an inner ring fit slidably around the reduced diameter shaft portion of the stepped shaft, and a cylindrical outer ring member surrounding the shaft, a plurality of balls of the first row interposed between the first inner raceway formed on the outer periphery of the inner ring and the first outer raceway formed on the inner periphery of the outer ring member, and a plurality of balls of the second row interposed between the second inner raceway formed directly on the outer periphery of the larger diameter shaft portion and the second outer raceway formed on the inner periphery of the outer ring member, the bearing apparatus being characterized in that:
the outer ring member includes upper and lower portions on the inner periphery of which is provided with the first and the second outer raceways respectively and a central portion therebetween,
a squeeze ring of the same material as that used in forming the outer ring member or of any other material of substantially the same factor of linear thermal expansion as that of the outer ring member is press fit around the outer periphery of the central portion of the outer ring member to elastically deform the outer ring member inwardly to form an inwardly protruding squeezed portion,
wherein the inner ring is secured to the shaft with applying an appropriate pre-load thereon, and
the outer diameter of the inner ring is identical with that of the larger diameter shaft portion of the stepped shaft, and the balls of the first row are identical in their diameter with that of the balls of the second row.
The balls made of ceramic material are used.
In the compound bearing apparatus of an embodiment in accordance with the present invention, a thin walled reduced outer diameter portion is formed around the outer periphery of the central portion of the outer ring member, and the squeeze ring is press fit around the reduced outer diameter portion.
In the compound bearing apparatus of another embodiment in accordance with the present invention, the outer ring member includes the first and the second sleeve outer rings adjacent axially with each other, each of the first and the second outer raceways is formed on the inner surface of the first and the second sleeve outer rings respectively, thin walled reduced outer diameter stepped portions are formed around adjacent end portions of the first and the second sleeve outer rings, and the squeeze ring is press fit around the reduced outer diameter stepped portions.
In the compound bearing apparatus of the other embodiment in accordance with the present invention, the outer ring member includes the first and the second sleeve outer rings adjacent axially with each other, each of the first and the second outer raceways is formed on the inner surface of the first and the second sleeve outer rings respectively, thin walled reduced outer diameter stepped portions are formed around adjacent end portions of the first and the second sleeve outer rings, and each of the first and the second squeeze rings is press fit around the reduced outer diameter stepped portions respectively.
In the compound bearing apparatus of the further embodiment in accordance with the present invention, the squeeze ring is formed on the inner periphery thereof with a thick walled reduced inner diameter portion having an inner diameter smaller than the outer diameter of the outer ring member, an axial width of the thick walled portion is smaller than the spacing between two rows of outer raceways, and the outer ring member is urged by the reduced inner diameter portion of the squeeze ring.